Using phase Doppler anemometry & high speed imaging to analyze MDI spray plume dynamics

Characterisation of inhalation aerosols focuses in the first instance on aerodynamic particle size, which is measured using cascade impactors. The aerosol must contain large quantities of particles in the respirable size range 1-5 m. Deposition on impactor stages depends on the velocity of the particles as well as their size. Pressurised metered dose inhalers (pMDIs) produce very fast-moving spray plumes, so it is important to understand the dynamic nature of droplet formation processes and spray plumes. This paper presents a selection of findings from an optical diagnostics study of aerosol plumes generated by a Bespak 630 series actuator in conjunction with a series of HFA134a placebo formulations containing ethanol up to 20% w/w. Spray plume dynamics in the vicinity of the spray orifice and further downstream were characterised using phase-Doppler anemometry (PDA), high-speed imaging and particle image velocimetry (PIV). The findings of the work demonstrate the complementary capabilities of these instruments. PDA provides simultaneous values of mean droplet size and velocity (and their associated statistics), but it is time-consuming to sample a sufficient number of locations to characterise the rapidly changing spray plume. PIV, on the other hand, provides information on entire flow fields albeit at lower spatial and temporal resolution. PIV and PDA data for the velocity of various spray plumes were found to be in good agreement, which validates both techniques. High-speed imaging also captures the overall characteristics of the plume. The diffraction limit of the optical configuration used for imaging is around 10 m, so it is not possible to observe respirable droplets individually. However, the dynamics and trajectories of larger droplets can be studied. These larger droplets were found to be produced by highly localised atomisation processes, so the resulting droplets can be easily missed or undersampled in PDA surveys. These results suggest that further research on pMDI sprays with these combined tools will provide useful insights into the processes responsible for changes in droplet size and velocity, and can be expected to make a major contribution to improving the development of the next generation of pMDI inhalers

Transient aerodynamic atomisation model to predict aerosol droplet size of pressurised metered dose inhalers (pMDI)

Pressurised metered dose inhalers (pMDI) produce large numbers of droplets with size of smaller than 5 μm to treat asthma and other pulmonary diseases. The mechanism responsible for droplet generation from bulk propellant liquid is poorly understood, mainly because the small length scales and short time scales make it difficult to characterise transient spray formation events. This paper describes the development and findings of a numerical atomisation model to predict droplet size of pharmaceutical propellants from first principles. In this model, the velocity difference between propellant vapour and liquid phase inside spray orifice leads to formation of wave-like instabilities on the liquid surface. Two variants of the aerodynamic atomisation model are presented based on assumed liquid precursor geometry: (1) cylindrical jet-shaped liquid ligaments surrounded by vapour annulus, (2) annular liquid film with vapour flow in the core. The growth of instabilities on the liquid precursors surfaces and the size of the subsequently formed droplets is predicted by numerical solutions of dispersion equations. The droplet size predictions were compared with Phase Doppler Anemometry (PDA) data and the predictions were in good agreement with the number mean diameter D10, which is representative of the respirable droplets. The temporal behaviour of droplet size production was captured consistently well during the period of the first 95% of the propellant mass emission. The outcome of our modelling activities also suggests that, in addition to saturated vapour pressure of the propellant, its viscosity and surface tension are also key properties that govern pMDI droplet size

Multi-physics theoretical approach to predict pMDI spray characteristics

Continued success in treatment of asthma and COPD requires development of new formulations, which may alter spray characteristics and atomisation quality of atomiser devices such as pMDI. Fundamental understanding of the underlying physical phenomena and the dynamic nature of pMDI aerosol plumes is essential to maintain pMDI device atomisation quality. In this paper, we describe a simulation of pMDI aerosol generation and plume development using a model of two-phase flow and atomisation of HFA134/ethanol formulation. The model is implemented within a CFD simulation to study the dynamic aerosol development and predict spray velocity and temperature. The CFD result shows plume velocity slows down over a relatively short distance and droplet temperature settles at a steady value of 291 K approximately at a distance of 30 mm from the spray orifice. This means that droplets reach their final size before reaching the exit of the mouthpiece

The effect of actuator nozzle designs on the electrostatic charge generated in pressurised metered dose inhaler aerosols

Purpose To investigate the influence of different actuator nozzle designs on aerosol electrostatic charges and aerosol performances for pressurised metered dose inhalers (pMDIs). Methods Four actuator nozzle designs (flat, curved flat, cone and curved cone) were manufactured using insulating thermoplastics (PET and PTFE) and conducting metal (aluminium) materials. Aerosol electrostatic profiles of solution pMDI formulations containing propellant HFA 134a with different ethanol concentration and/or model drug beclomethasone dipropionate (BDP) were studied using a modified electrical low-pressure impactor (ELPI) for all actuator designs and materials. The mass of the deposited drug was analysed using high performance liquid chromatography (HPLC). Results Both curved nozzle designs for insulating PET and PTFE actuators significantly influenced aerosol electrostatics and aerosol performance compared with conducting aluminium actuator, where reversed charge polarity and higher throat deposition were observed with pMDI formulation containing BDP. Results are likely due to the changes in plume geometry caused by the curved edge nozzle designs and the bipolar charging nature of insulating materials. Conclusions This study demonstrated that actuator nozzle designs could significantly influence the electrostatic charges profiles and aerosol drug deposition pattern of pMDI aerosols, especially when using insulating thermoplastic materials where bipolar charging is more dominant

The effect of active pharmaceutical ingredients on aerosol electrostatic charges from pressurized metered dose inhalers

Purpose. This study investigated the effect of different active pharmaceutical ingredients (API) on aerosol electrostatic charges and aerosol performances for pressurized metered dose inhalers (pMDIs), using both insulating and conducting actuators. Methods. Five solution-based pMDIs containing different API ingredients including: beclomethasone dipropionate (BDP), budesonide (BUD), flunisolide (FS), salbutamol base (SB) and ipratropium bromide (IPBr) were prepared using pressure filling technique. Actuator blocks made from nylon, polytetrafluoroethylene (PTFE) and aluminium were manufactured with 0.3 mm nominal orifice diameter and cone nozzle shape. Aerosol electrostatics for each pMDI formulation and actuator were evaluated using the electrical low-pressure impactor (ELPI) and drug depositions were analysed using high performance liquid chromatography (HPLC). Results. All three actuator materials showed the same net charge trend across the five active drug ingredients, with BDP, BUD and FS showing positive net charges for both nylon and PTFE actuators, respectively. While SB and IPBr had significantly negative net charges across the three different actuators, which correlates to the ionic functional groups present on the drug molecule structures. Conclusions. The API present in a pMDI has a dominant effect on the electrostatic properties of the formulation, overcoming the charge effect arising from the actuator materials. Results have shown that the electrostatic charges for a solution-based pMDI could be related to the interactions of the chemical ingredients and change in the work function for the overall formulation

High-speed laser image analysis of plume angles for pressurised metered dose inhalers: the effect of nozzle geometry

The aim of this study is to investigate aerosol plume geometries of pressurised metered dose inhalers (pMDIs) using a high-speed laser image system with different actuator nozzle materials and designs. Actuators made from aluminium, PET and PTFE were manufactured with four different nozzle designs: cone, flat, curved cone and curved flat. Plume angles and spans generated using the designed actuator nozzles with four solution-based pMDI formulations were imaged using Oxford Lasers EnVision system and analysed using EnVision Patternate software. Reduced plume angles for all actuator materials and nozzle designs were observed with pMDI formulations containing drug with high co-solvent concentration (ethanol) due to the reduced vapour pressure. Significantly higher plume angles were observed with the PTFE flat nozzle across all formulations, which could be a result of the nozzle geometry and material’s hydrophobicity. The plume geometry of pMDI aerosols can be influenced by the vapour pressure of the formulation, nozzle geometries and actuator material physiochemical properties

SAUL fabrication project: building a civic platform at St. Munchin’s Church of Ireland

Saul fabrication project was the first build project to be under-taken by the School of Architecture in the University of Limerick. A group of 6 students collaborated in a "7 week design, 7 week build" to transform Old St. Munchin's Church, King's Island, Limerick into a multi-functional space

Application development using modeling and dynamical systems analysis

Research on context aware systems is handicapped by the lack of readily available large scale data sets, as well as by the lack of tools by which researchers can interact effectively with such data sets across a range of scales and granularities. We show how virtual reality combined with a dynamical systems analysis approach can start to address these gaps. Simulation allows for generation of simulated sensor data at runtime and actuations of entities in the virtual world. The ease of sensor deployment and configurations in a simulated environment allows for rapid reconfigurations enabling generation of the required large scale data sets for analysis. Using these data sets, dynamical systems analysis can determine if a given application is functioning in a manner that is deemed to be correct

Comparing herbaceous plant communities in active and passive riparian restoration

<div><p>Understanding the efficacy of passive (reduction or cessation of environmental stress) and active (typically involving planting or seeding) restoration strategies is important for the design of successful revegetation of degraded riparian habitat, but studies explicitly comparing restoration outcomes are uncommon. We sampled the understory herbaceous plant community of 103 riparian sites varying in age since restoration (0 to 39 years) and revegetation technique (active, passive, or none) to compare the utility of different approaches on restoration success across sites. We found that landform type, percent shade, and summer flow helped explain differences in the understory functional community across all sites. In passively restored sites, grass and forb cover and richness were inversely related to site age, but in actively restored sites forb cover and richness were inversely related to site age. Native cover and richness were lower with passive restoration compared to active restoration. Invasive species cover and richness were not significantly different across sites. Although some of our results suggest that active restoration would best enhance native species in degraded riparian areas, this work also highlights some of the context-dependency that has been found to mediate restoration outcomes. For example, since the effects of passive restoration can be quite rapid, this approach might be more useful than active restoration in situations where rapid dominance of pioneer species is required to arrest major soil loss through erosion. As a result, we caution against labeling one restoration technique as better than another. Managers should identify ideal restoration outcomes in the context of historic and current site characteristics (as well as a range of acceptable alternative states) and choose restoration approaches that best facilitate the achievement of revegetation goals.</p></div